Background: Young men who have sex with men (YMSM) are at exceptionally high risk for HIV infection in the United States, accounting for 72% of new HIV infections among all persons aged 13 to 24, and 30% of new infections among all MSM. Increasing awareness of HIV status and expanding access to PrEP for high risk HIV-uninfected YMSM is essential for reducing the population burden of disease; however, overall rates of testing and PrEP uptake among young adults are suboptimal. Mobile app use is common among YMSM in the U.S., and thus they offer unique opportunities for HIV prevention interventions to be provided to YMSM via a modality that is familiar and discrete. Overview: Informed by our formative research with YMSM in the US and guided by the Social Cognitive Theory (SCT), our team developed ?MyChoices?, a mobile app aimed to increase HIV testing and PrEP uptake among YMSM in the U.S. MyChoices? uses interactive capabilities and reminder systems to support self-regulation and self-efficacy around HIV testing and PrEP uptake?core factors that influence behavior change in the SCT model. We propose to refine and pilot test the ?MyChoices? app, laying the groundwork for an R01 efficacy trial as part of this same iTech U19 application. We propose to: (Aim 1) conduct theater testing with YMSM to refine ?MyChoices? for HIV/STI testing and PrEP uptake promotion. ?MyChoices? will be demonstrated in up to 4 groups with up to 20 YMSM at two iTech clinical research sites to obtain detailed feedback on displays, features and functions of the ?MyChoices? app. Data will be used to make final app refinements; (Aim 2) conduct a technical pilot to optimize MyChoices app functionality, technical performance, and user satisfaction. The app will be piloted with a group of up to 15 YMSM at two iTech clinical research sites for a 2-month period. Participant exit interviews will be used to finalize all study procedures, questionnaire and intervention manual for use in the next phase (RCT; Aim 3); (Aim 3) conduct a pilot RCT to evaluate the feasibility and acceptability of MyChoices to increase HIV/STI testing and PrEP uptake among YMSM. 60 YMSM at two iTech sites (30 at each site) will be enrolled and randomized (2:1) to one of two conditions: a) MyChoices app; or b) control condition which consists of links to local HIV/STI testing resources. The primary outcomes will be feasibility and acceptability of the app over 6 months. We will also assess preliminary efficacy of the app to increase HIV testing (via self-report) and PrEP uptake (via self-report). Innovation: If the app proves to be efficacious in a future efficacy trial (proposed as part of this iTech U19), this innovative technology has the potential to reach a large population of at-risk YMSM across the United States, increase HIV testing and PrEP uptake among those at highest risk and reduce the burden of HIV in this population.